“The stationary bunting type of motion is that which would be demanded by the passage of the spermatozoon through the egg membrane which has been so often observed in the lower animals. This very plausible explanation is, however, necessarily theoretical and must always remain so, as the conditions which surround the specimen on the field of the microscope vary in so many respects from those in which it accomplishes conjugation in the course of nature; but the practical importance of the study of types of motion is not affected by their explanation.” The duration of motility is a variable factor, dependent entirely upon the environment in which the spermatozoa are placed. Within the body they usually survive at least a week. One author describes a case in which he found living sperms in a woman who stated that coition had not been experienced for three and one-half weeks. It has been stated with regard to human sperms, that their motion should continue or be capable of being re-established for twelve hours. Cary (35) states, “first, that in their proper medium and at the body temperature the viability of the sperm cells may extend over a period of a few days; second, that their prolonged vitality is probably dependent upon the normal lime salts of the prostatic fluid; third, that the sustaining power of the seminal fluid is increased by its union with the normal secretion of the female genital tract.” After death of the male animal they retain their motility in the genital tract for twenty-four to forty-eight hours. Wolf (36) worked on this problem in rabbits, and summarizes as follows: “The motility of rabbit spermatozoa can be preserved for at least nine days by placing the juice of the epididymis in the Tyrode solution which had been buffered and to which glucose had been added. The solution is adjusted to a pH of about 7.4. Oxygen is passed in and a suitable amount of sodium bicarbonate added. The preparation must be kept at a temperature near the freezing point of water.” Under ordinary conditions motility persists outside the body only a few hours after ejaculation, but if the semen is kept quite cool till the time of examination on a warm stage, motility should be capable of being restored in at least a fair percentage of the sperms for twenty-four to forty-eight hours. The cells are more sensitive to heat than to cold, and even to dilute acids more than to alkalies.